Steel alloy and process of making the same



Patented at. 21 192s.

UNITED STATES,

, PATENT OFFICE.

THOMAS .A. KOORKANN', OF MILWAUKEE, WISCONSIN, ABBIGN OB '10 ml comm- TION', F HILWAUKEE, WISCONSIN A. OOBPORA'IIQN Q1 WIBCOKSIN.

PEEL ALLOY" PROCESS OI MAKING THE sum.

Ho Drawing.

present on the surface of the molten metal- 1n the pourin ladle, but is also found on the surface 0 the metal after it has been cast in the mold. y

In the process of pourin thisfilm car'- ries with it entrained san and other ex-' traneous matter, which results in imperfec-- tions in the surface of the casting. In order to remove these surface defects, excessive.

machining of the casting is necessary.

castings are encountered particularly in the case 0 alloy steels which contain chromium and other similar alloying elements It is one of the ob'ects of my invention to so treat the steel t at the film of oxide forming on the surface of the molten metal and causing surface defects in the castin is substantially eliminated, with the resu t that the amount of machinin necessary to give the castin a perfect nish is very lar ely decrease I V have found that this result may be accomplished by the use of the addition of a relatively small quantity ofboron, which, 5 particularly in the case of alloys in which chromium is used, forms a very fluid flux, which is without deleterious effect on the surface of the casting.

I have also found that a further advan- 40 tage resulting from the use of boron is that the size of the risers can be eatly reduced in obtaining solid castings, t e effect of the boron being to lower t e temperature at which the steel becomes completely solid so 5. that the risers can be kepti 'molten condition for a longer time, thus allowing the addition of molten metal as the level of the molten metal in the risers c'bndi tion which is normally brought about as the 59 metal solidifies in the casting proper.

A further object of my inventionis-torovide an alloy having the desirable surma features pointed. out above, and which,

oxide forms on the surface of the.

The above difiiculties of making I good "the boron goes into the slag, formlng a very suitable alloy,[

before pouring.

I Application fled November 11, 1926. Serial No. 147,852.

particularly when heat treated, will present great" resistance to wear and abrasion.

The various objects of my invention are accomplished in the manner which I shall I now describe.

The steel is preferably made in an acid electric furnace, the desired alloying elements being preferably added in the form of ferro al oys to give required analysis of the finished material.

Shortly before the tapping of the furnace, I add to the charge boron, either in the form of ferro-boron, or other suitable alloy, such as boron manganese. I have found that approximately .40 per cent boron figured on t e entire furnace charge gives satisfactory results, although the amount of boron addedto the char e ma vary between .20 and 2.6 er cent wit out 'eparting from the spirit 0 m invention. Particularly in the presence 0 chromium, a large part of fluid. slag. At the same time, it serves to eliminate from-the, metal impurities, such as entrained oxides. The boron contained in the finished steel is ordinarily found to be between .05 and .20.

Although I have described the use of boron particularly as a furnace addition, the boron in the form of ferro-boron, or other ma if desired, be added 1n the ladle. f the is done, sufficient time should be allowed for the uniform alloyin of a portion of the boron with the stee I and the metal should, of course, be allowed to cool to the proper pouring temperature In order to cause a thorough mixture of the boron with the steel, I refer to stir the molten metal either in the mace or in the ladle.

I have found that a typical analysis of the alloy in connection with which my improved rficess may be advantageously used, is as o ows:

P0! cent.

and 20 per cent.

In the finished casting, there would also be found from about .05 to about .20 per cent boron, as previously pointed out, although in some cases this amount may be advantageously increased up to approximately one per cent. a

Considerable variations may be made from the typical anal sis which I have given without eparting mm the spirit of my invention. For example, carbon may be between 1.2 and 3.5 per cent; chromium between 8 In place of cobalt and molybdenum, as given in the typical analysis above mentioned, I may use tungsten, uranium, zirconium or titanium, either with or without cobalt or molybdenum, or both, the combined percentage of the elements cobalt, molybdenum, tungsten, uranium, zirconium and titanium being approximately between one and two per cent.

Castings which are made of the alloy which I have described arevery hard and practically unmachinable, but upon annealing may be readily machined. It has been found that these castings may be heat treated or annealed without distortion and are ractically immune from danger of crack- 1ng. Rockwell hardness values O63 are obtainable by air cooling without quenching or use of a cooling blast.

The physical properties of the heat treat ed castings are tensile strength about 125,000 pounds per square inch, and compressive strength about 420,000 pounds per square inch.

The heat treated castings made according to my invention have high resistance to abrasion and are particularly adapted for use as tools such asformin dies, and the like.

It has been found t at the hardness and resistance to abrasion extends through the entire mass of the heat treated castings and is not confined to the surface thereofa feature which is most valuable and desirable in connection with tools such as dies, which are frequently redressed.

The steel may also be heat treated so that it will be left in the austenetic condition, and therefore non-magnetic.

It is also possible to forge steel made in accordance with my invention; and in the hardened condition, I have found that such forgings have a tensile strength of approximately 220,000 pounds'per square inch.

I have also found that a steel made in accordance with my invention does not have its hardness altered or impaired by subjecting the hardened steel to temperatures up to 1100 degrees Fahrenheit.

It will be apparent to those skilled in the art that many changes could be made in the details of the invention which I have described without departing from the spirit or scope of my invention.

Iclaim:

A steel alloy of substantially the following composition; approximately carbon 1.50%, chromium 13%, cobalt .70%, molybdenum 1.10%,boron .05 to 20%.

Signed at Milwaukee, Wisconsin, this 1st day of November, 1926.

THOMAS A. MOORMANN. 

